Multiposition rear projection display apparatus

ABSTRACT

A 48 character, 24 lamp rear projection, incandescent lamp powered display unit. The unit utilizes a flat movable mask incorporating the 48 characters to be displayed and a unique optical system to project the selected character on the unit display screen without distortion. An actuating mechanism for moving the mask between one of two positions is provided, the movement of the film being correlated with energization of a predetermined one of the lamps to produce the desired display. The display screen is movable to provide a push button arrangement which is to be actuated by the operator primarily in response to symbols or characters displayed thereon.

United States Patent [1 1 Farnden et a1.

MULTIPOSITION REAR PROJECTION DISPLAY APPARATUS Inventors: Robert W. F arnden, Sepulveda;

Roger Silverstone, Sunland; John E. Hendricks, Encino, all of Calif.

Assignee: Industrial Electronic Engineers, lnc.,

Van Nuys, Calif.

Filed: July 20, 1971 Appl. No.: 166,225

Related US. Application Data Continuation of Ser. No. 819,609, April 28, 1969, abandoned.

US. Cl. 353/25, 353/74 Int. Cl. G03b 21/10 Field of Search 353/36, 37, 40, 45,

References Cited UNITED STATES PATENTS 7/1967 Gessel 353/36 X Sept. 25, 1973 3,460,135 8/1969 Gardner .l 340/378 3,096,512 7/1963 Hollowich et al..... 3,201,784 8/1965 Hendricks et al..... 3,244,071 4/1966 Gumpertz 353/36 Primary ExaminerHarry N. Haroian Att0rneySmyth, Roston & Pavitt 5 7 ABSTRACT A 48 character, 24 lamp rear projection, incandescent lamp powered display unit. The unit utilizes a flat movable mask incorporating the 48 characters to be displayed and a unique optical system to project the selected character on the unit display screen without dis tortion. An actuating mechanism for moving the mask between one of two positions is provided, the movement of the film being correlated with energization of a predetermined one of the lamps to produce the desired display. The display screen is movable to provide a push button arrangement which is to be actuated by the operator primarily in response to symbols or char- 'acters displayed thereon.

24 Claims, 9 Drawing Figures PATENT ED strzsma 30m 1 1 E SHEET 3 0F 4 PATENTEDSEPZSIBH sumac? 4 1 MULTIPOSITION REAR PROJECTION DISPLAY APPARATUS This application is a continuation of application Ser. No. 819,609 filed 4/28/69 and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to character projection units of the type employed for selectively displaying different characters on a projection screen and in particular to improvements in the lenses used with such units.

Light powered, character rear projection units are generally employed in large multiples, to display multidigit numbers, words and other symbols. Typically, each projection unit incorporates a rectangular viewing screen which occupies a space in an overall panel display reserved for a single letter, digit or symbol. By selectin'g a particular number or letter to be projected by each unit, different multi-digit numbers and words may be displayed. A prime requirement is that each projection unit be capable of displaying any one of a selection of letters or numerals as, for example, the numerals zero through nine. This requirement is compounded by a competing requirement of compactness resulting from the fact that the display units must be located close together so as to provide a conventional spacing between the digits and letters of multi-digit numbers and words. The problem of compactness is solved to a great degree by the employment of lens plates which integrallyincorporate and support at the proper physical location the individual lenses of each type, e.g., the collecting lens in a unit providing a multiplicity of converging projection systems as described in US. Pat. No. 3,041,600.

It is presently conventional in display units of the type just described to provide a collecting lens, condensing lens and projection lens together with a light source and a character forming mask in each 'of the plurality of converging projection systems. The primary objectives in the design of these units is to achieve maximum light intensity and character resolution on the viewing screen.

In US. Pat. No. 3,332,318 is described an improvement of the basic lens system referred to above. In this improvement the single condensing lens is replaced by a doublet pair of lensescomprising a collimating lens and a condensing lens with a character mask located between them. The advantage of such an arrangement is increased brightness of the image displayed on the projection screen coupled with reduced magnification requirements of the individual lenses in the system, reduced distortion of the images projected on the screen and the ability to use characters of a larger size increasing the total amount of illumination which can be transmitted to the projection screen.

To obtain uniform brightness, magnification and size of each character or symbol displayed by such projection units, the light sources and the lens plates are constructed in a spherically curved configuration with the center of curvature located at the projection screen. The character mask is typically a piece of film which is opaque over its surface area except for a uniform distribution of transparent character outlines. The film is normally supported by a lens or combination of lenses of the system and assumes the physical configuration of these lenses. Thus in a spherical optical system the film is also spherical in configuration with its center also being located at the projection screen.

In such conventional systems a number of character outlines and light sources are provided on a l for 1 basis. The particular character to be projected depends upon which individual source of the plurality of light sources is energized. To increase the total number of characters which can be projected with a display unit of a given projection screen size, efforts have been made to miniaturize each individual projection system thereby permitting an increase in the total number of projection systems which can be incorporated in the unit. It is difficult, however, to reduce the physical size of the light sources beyond a certain point and hence considerationhas been given to increasing the character-light source ratio by increasing the total number of characters operatively associated with a given one of the light sources.

SUMMARY OF THE INVENTION A solution to the problems outlined above is presented by the present invention which provides a multiple symbol rear projection display system comprising a plurality of light sources disposed about a center line of the display system, a projection screen located at the end of the system opposite the light sources and an optical projection system located between each of the light sources and the projection screen, each projection system including a light collecting lens, a condensing lens and a projection lens disposed along an optical axis extending between each of the light sources and the projection screen. Means are provided for supporting the individual light sources, a first lens plate supports the individual light collecting lenses and a second lens plate supports the individual condensing lenses. Means are also provided for supporting the projection lenses such that the principal points of each of the projection lenses lie in a plane perpendicular to the center line of the display system and a character mask is located on the side of the projection lenses opposite the projection screen. The character mask includes at least two characters for selective display by at least one of the optical projection systems on the projection screen. Means for moving the character mask between a first and second position corresponding to the display of the selected character is also provided.

The invention also provides a backlighted display apparatus comprising a housing, a viewing screen, an optical projection system mounted within the housing for selectively projecting'an image on the viewing screen, the projection system including a light source. A character mask having at least two character outlines disposed thereon is provided along with means operatively associated with the character mask to translationally move the mask for selectively centering one of the character outlines with respect to the projection system. Mounting means coupled to the housing for mounting the viewing screen for limited movement relative to the housingin response to a force supplied to the viewing screen are provided, the mounting means including means for normally mounting the viewing screen in a predetermined position relative to the housing whereby an image is focused by the projection system on the viewing screen. Finally there is provided means operatively associated with the viewing screen for sensing the movement of the viewing screen to actuate means for selectively energizing the projection system and the means for selectively moving the mask.

By the present invention the number of characters which can be displayed by a rear projection display system (readout device) having a given number ofindividual light sources is increased (i.e., the character-light source ratio is increased) by placing additional characters in the spaces on a character mask between the location of characters as they would be placed in a conventional mask. In some instances this may require a reduction in the individual character or symbol size and relative repositioning of the two or more characters associated with a particular light source. To project each character without increasing the number of lamps, means for centering each character in one of the individual projection systems is needed. One approach is to physically move a character mask between two or more positions.

With the conventional optical systems referred to above, movement of the film is difficult because its spherical shape does not readily lend itself to easy translational motion. Assuming a film mask in such a spherical configuration could be supported so as to be movable, the mechanical arrangement for moving such a film would necessarily be complicated requiring a considerable amount of space within the overall package housing the display unit.

The present invention eliminates the preceding problem by providing a mechanism which utilizes a character mask in a flat or planar configuration which is used with an optical system which, in a preferred embodiment, generally retains the spherical curved configuration of a type of conventional rear projection display systems. In accomplishing this result the optical axes at the character mask plane are moved slightly and reestablished without changing the position of the aiming point at the screen, so that optical centers are equidistant in a plane section perpendicular to the centerline of the display apparatus. Each of the characters is spaced equidistantly relative to adjacent characters to enable one shift value of the mask to fully change all positions equally. Equal magnification of each projection system is achieved by mounting the projection lenses in such fashion that the principal points of each of the individual projection lenses lie in a common plane which is perpendicular to and intersects the centerline of the display apparatus. The magnification of the character depends primarily upon the positional placement of the projection lens between the character mask and the screen. Placing the principal points of the projection lenses in a common plane maintains an identical ratio between the distance of each individual character mask and its projection lens and the distance of each projection lens and the aiming point at the screen thus achieving the desired equality. In the same way, distortion or unequal magnification, is kept to a minimum. This is due to all light ray paths through the principal point of each projection lens drawn from the character mask to the screen, with mask and screen lying parallel to each other, being divided into essentially equal ratio proportions. Since magnification primarily depends upon this ratio of distance or lens position between character and film, maintaining equal magnification holds distortion to a minimum.

To shift the flat character mask between two or more selectable positions the apparatus incorporates an actuating mechanism which utilizes at least one pair of elec tromagnetic coils and a mechanical linkage extending from the character mask to a position operatively associated with the coils, the linkage having the configuration of a detent over-center bistable mechanism such that when a coil other than the coil previously energized is energized, the linkage travels from a previously stable position to a new operating position.

A preferred embodiment of the invention includes a movable viewing screen and also includes switch means associated therewith for generating control signals responsive to displays on the projection screen for actuating remote equipments.

By the present invention, a display apparatus is provided which doubles the number of symbols or characters which can be projected by the apparatus for a given number of light sources used with the apparatus. By increasing the degrees of freedom of movement of the character mask, e.g., adding lateral translational displacement to vertical translational displacement, the number of selectable messages can be quadrupled relative to the number of light sources provided. The film positioning mechanism provided as a part of the apparatus provides precise positioning of film messages within the optical system while the positioning mechanism travel is not restricted. The over-center bistable linkage enables positioning of the armature in a manner which reduces power requirements for the next actuation and automatically lifts the previously actuated side of the armature off of the core and coil polepiece. The bistable mechanism further provides vibration-proof film position by loading the film against the periphery of the lens which is used to support it. With the optical system arranged in a non-spherical configuration, suitable optical provisions in the form of additional optical elements, e.g., prisms or mirrors can be provided to direct and center the projected characters on the screen.

BRIEF DESCRIPTION OF THE DRAWINGS These and other advantages of the present invention will be better understood by reference to the following figures in which:

FIG. 1 is a side elevational view, partially cut away, of a display apparatus according to the present invention;

FIG. 2 is a rear elevational view taken along lines 22 of FIG. 1, also partially cut away;

FIGS. 3A-D are diagrammatic views of the various principal positions of the film actuating mechanqsm;

FIG. 4 is a side elevational view of the optical system of the present invention as provided in a long focal length projection system;

FIG. 5 is a side elevational view of the optical system of the present invention as provided in a short focal length projection system;

FIG. 6 is a schematic block diagram of a control system employing the display apparatus of the present invention;

FIG. 7 is an elevational view of the character mask and auxiliary mask means utilized with one embodiment of the present invention;

FIG. 8 is a side elevational view of the character mask, auxiliary masking means, condensing lens plate and mask holding plate; and

FIG. 9 is a circuit diagram illustrating the manner in which a typical set of light sources are electrically connected to a source of electrical power.

DESCRIPTION OF A SPECIFIC EMBODIMENT Referring now to FIG. 1, there is shown in side elevation a display apparatus according to the present invention. The apparatus comprises a housing in which is located a plurality of light sources 12 disposed at one end of the apparatus and a projection screen 14 located at the end of the apparatus opposite the light sources. Each of the plurality of light sources 12 is associated with an individual optical projection system 16 located between the light sources and the projection screen. Each optical system 16 includes a light collecting lens 26, a light condensing lens 28, a film and mask holding plate 22 and a projection lens 30. In the embodiment of FIG. 1 the lenses of each type are supported by a lens plate, i.e., with the exception of the film and mask holding plate, a light collecting lens plate 18, a light condensing lens plate 20, and a projection lens plate 24 integrally incorporates a plurality of lenses, the number of lenses in each of the lens plates corresponding to the number of individual projection systems in the display apparatus. Each of the lenses in the various lens plates performs the function in its optical projection system for which the lens is named, namely, light collecting, light condensing and light projecting, respectively. Each of the respective lens plates positions and supports the individual lenses in the proper position along an optical axis extending from the light source associated therewith to the projection screen. In the embodiment of the apparatus of FIG. I equidistant spacing of like elements in each system and hence uniform size, brightness and positioning of the images projected by each of the various optical systems on the projection screen are obtained by providing lens plates 18, 20 and 22 with a spherical curvature with the center of curvature being located at the center 32 of the projection screen.

As distinguished from the shape imparted to lens plates 18, 20 and 22 in FIG. 1, projection lens plate 24 is provided in a configuration such that the principal points of each of the individual projection lenses 30 lie in a common flat plane which is disposed perpendicular to the center line 34. The embodiment of the optical system shown in FIG. 1 will be referred to herein as one having a long focal length. A more complete description of the projection lenses 30 and projection lens plate 24 and the interrelation of various points and planes of these lenses is provided in conjunction with is located between condensing lens plate 20 and a mask holding plate 22. Mask 36 may be a single sheet or strip of film having a plurality of transparent characters surrounded by an opaque material. Bracketing mask 36 is a pair of auxiliary masking elements 38. The character mask 36 and masking elements 38 are disposed between and supported by lens plate 22in a detent 39 (see FIG. 8) which is defined by a shoulder 41 extending around the periphery of plate 22. Character mask 36 is provided with a width dimension corresponding to the width dimension of masking elements 38 while its length dimension 36 is made slightly shorter than the corresponding dimensions of masks 38 to permit mask 36 to be moved between two operating positions under the influence of a film actuating arm 40 to center one of the two sets of symbols in the projection system of the apparatus. Cne end of actuating arm 40 engages character mask 36 at a tongue 42 projecting downwardly from the mask. The relationship of the character mask 36, masking elements 38 and film and mask holding plate 22 will be discussed in more detail in conjunction with the discussion of FIGS. 7 and 8.

The film actuating portion of the display apparatus utilizes a pair of electromagnetic coils 44 and 46 for actuating an armature 48 (shown in both a solid and ghosted position to illustrate one set of operating positions) pivotally mounted between the coils at pivot 50. Armature 48 is connected to film actuating arm 40 by means of a spring biasing member 52 which is connected at one end to one extremity 78 of armature 48 and at its other end to a point 53 intermediate the ends of film actuating arm 40. Film actuating arm 40 is mounted at the end opposite its point of engagement with mask 36 at a pivot 54. By supplying electric power to one of the two coils 44 and 46, armature 48 is attracted toward the energized coil which in turn produces a pivoting of film actuating arm 40 about its pivot 54 and vertical translational motion of character mask 36 between two predetermined positions. Coils 44 and 46, armature 48, coil spring 52 and film actuating arm 40 combine to form a detent bistable mechanism operating on an overcenter principal such that when either of the coils is energized the armature moves or pivots over toward the energized coil and remains against or relatively closely positioned with respect to that coil until the second coil is energized.

Projection screen 14 is pivotally mounted for limited movement at point 56 and by means of a tongue 58 engages a plunger 60. When pressure is exerted against the screen causing it to move to the ghosted position, a contact ring 62 is caused to move in a direction generally parallel to the center line 34 of the display apparatus to thereby make electrical contact with contacts 64. In this manner the display apparatus can be utilized as a switch for transmitting actuating signals to remotely located apparatus in response to the character or symbol projected on screen 14. Plunger is spring biased by means of coil spring 66 to cause the plunger and screen to return to a normal, predetermined at rest position shown in solid lines in FIG. 1 when the pressure is removed from the face of screen 14, the position corresponding to the focal point of the projection systems of the display apparatus.

Power is supplied to the various light sources 12 of the display apparatus by means of a printed circuit board 68 having a male portion 69 which is adapted to mate with a corresponding female connector (not shown) to supply electric power through electrical conductors 70 to the light sources 12. As shown in FIGS. 1 and 2, a plurality of diodes 72 are provided in the electric circuit between conductors 70 and lamp bases 74. For reducing the number of conductors 70 the unit of the present invention is energized utilizing a split electrical ground design and feedback limiting diodes 72 together with electrical circuit connections to various lamps in pairs (see FIG. 9). A common input 73 is provided for each group of twelve lamps (shown as filaments 75) while a single retum line 79 is provided for corresponding pairs of lamps. Connected between the lamp and the return are diodes 72 to prevent current flowing through the selected lamp from flowing through other lamps on its way to the return line. Energization of the lamps using this arrangement must be provided on a DC basis.

Electrical connections to the lamp bases 74 from conductors 70 are provided by contacts 126 which are in electrical circuit continuity with conductors '70 and lamp bases 74. As shown the contacts generally have the shape of the letter Z of the alphabet and as arranged in the unit are spring loaded against the lamp bases. Each of the Z shaped contacts comprise an electrically conductive, resilient strip of material having a pair of base members and an interconnecting diagonal member extending between said base members. One base member is securely mounted on support 128 at the rear of the unit and the opposite base member is positioned so as to contact the lamp base 74 with which it is associated in an electrically continuous, spring loaded manner. The Z-spring design of the contacts thus provides maximum lamp contact reliability with only one pressure loaded contact point at the lamp base.

The details of the structure and operation of the film actuating mechanism will be better understood by reference to FIGS. 3A-D. In those figures are shown the four major operations positions of the armature 48. As coil 46 is energized, armature 48 is attracted to polepiece 76 and comes to rest in contact with that pol-epiece. In the course of its pivoting toward polepiece 76, armature 48 exerts a force on coil spring 52 causing film actuating mechanism 40 to pivot about point 54 thereby drawing the tongue 42 of the character film mask down to the down" film position and centering a first set of characters in the projection systems. When the supply of electrical energy to coil 46 is terminated removing the attractive force toward the polepiece 76, sufficient force is exerted by coil spring 52 which is under increased tension when the armature contacts a polepiece to cause armature 48 to be drawn away from the polepiece until pivot point 50 is aligned with points 78 and 53 where coil spring 52 engages the armature 48 and film actuating arm 40, respectively. At this point, the film actuating mechanism is at rest with the film in the down position.

When coil 44 is energized, armature 48 is attracted to polepiece 84 again exerting force on coil spring 52 causing film actuating mechanism 40 'to pivot about point 54, pushing film tongue 42 in an upward direction and coming to rest when armature 48 contacts polepiece 84. At this point the film is in the up position and a second set of characters are in projection positions. Disconnection of energy from coil 44 allows spring 52 to pull armature 48 away from polepiece 84 slightly to an at rest position with the film in the up position where again points 50, 78 and 53 are aligned.

The advantage of providing the at rest positions when the film mask is in the up or down positions enables closer positioning of the armature relative to the coil to be next energized and automatically lifts the previously actuated side of the. armature off the core and polepiece. Positioning the armature closer to the two coils reduces electrical power requirements when actuating the mechanism. Lifting the actuated side of the armature from the core and polepiece by spring biasing eliminates failures caused by residual magnetism which might tend to prevent and overcome operation of the film mechanism as the opposite coil is energized.

The film actuation system is additionally advantageous in that a flexible biasing means such as acoil spring link between the actuating mechanism armature and the film actuating arm provides precise positioning of film messages with the optical system. This is due to the fact that the shoulder 41 of the film and mask holding plate provides a positive stop for the film as it moves between its two operating positions while any over-travel in the mechanism is absorbed in the coil spring. Further, by loading the film against the lens flange (shoulder) in the at rest positions the detent, bistable film actuating mechanism provides vibrationproof film positioning and prevents vibration transmitted to the display apparatus from causing the film to jiggle or move whether the coils are energized or not.

The diagrams of FIGS. 4 and 5 illustrate the manner in which the display apparatus of the present system displays a number of projected messages which is double the actual number of fixed projection systems with which the apparatus is equipped. In one embodiment of the present invention it is now possible to obtain 48 messages from an optical system comprising 24 lamps and 24 optical projection systems. FIGS. 4 and 5 illustrate the manner in which this objective is accomplished in a long and a short focal length projection system respectively. In each system this is accomplished by increasing the thickness of the condensing lens plate 20 in comparison to the thickness of the condensing lens plate shown, for example, in U. S. Pat. No. 3,041,600 andlocating the film mask between the front and back surfaces of the lens. In a preferred embodiment of the present invention this is accomplished by in effect splitting the condensing lens plate into two plates, the second being plate 22, the film and mask holding lens plate. This enables the positioning of a flat character film mask 36 between the assembly of lens plates 20, 22 and within the spherical curvature of the assembly. The fiat geometric form of the film mask facilitates its vertical translational motion between its two operating positions. Auxiliary masking elements 38 bracket character mask 36 to complete the combination and prevent unwanted images from being projected on the display screen.

The combination of a flat character mask and a thickened, spherically curved condensing lens produces a variation from projection system to projection system of the display apparatus in the relative positioning of the individual character masks and the surfaces of its associated condensing lens. To compensate for the above variation, a projection lens plate 24 is provided and each of the individual projection lenses 30 of the projection lens plate is oriented relative to each other so that the principal points 86 of each one of the projection lenses lie in a plane 92 perpendicular to the center line 34 of the display system 11. Orienting the lenses in accordance with the foregoing requirement keeps the magnification of each of the projection systems of the display system uniform. Uniform magnification enables the provision of uniform message area sizes in the film mask so that the spaces between the characters of a mask used in a conventional projection system (US. Pat. No. 3,041,600) can be utilized to carry a second set of messages also of the same uniform size.

The individual projection systems thus project everything within the conical lighted area 88 with the exception that the auxiliary masks 38 screen out a portion of the cone of light to prevent the unwanted messages from appearing on the screen. To facilitate film movement between the up and down positions, the masks 38 are coated on the side adjacent the film with a friction reducing material such as poly-tetrafluorethylene. This has the further advantage of insuring that the film does not erode itself or the lenses and thus prolongs the useful life of the display system. As an alternative to the provision of auxiliary masks 38, masking may also be accomplished at the projection screen 14.

In the long focal length projection system of FIG. 4, the depth of field of the projected message is great enough to allow the individual lenses 30 to be integrally molded into a flat lens plate 24 with the principal planes 90 of each projection lens lying in a common plane 92 positioned at right angles to the display apparatus center line 34. In short focal length projection systems as typified by FIG. 5, the depth of field is restricted and when a flat projection screen is placed within the field, the projection lenses which would be canted with respect to the individual projection system center lines 94 werethe lens plate 24 shown in FIG. 4 used, would cause part of the projected message to be out of focus at the screen. To compensate, as shown in FIG. 5, the principal planes 90 of the individual projection lenses 30 are constrained to lie at right angles to the individual projection system center lines 94, thus placing the center of the projection field at the screen center 32 and bringing all of the message area into focus. Orienting the individual lenses 30 in this manner produces a variation from projection lens to projection lens in the distance from the center of the screen to the individual projection lens. To compensate, the curvature of each of the individual projection lenses is varied thus providing a projection lens plate asshown in FIG. wherein the principal points 86 of the projection lenses again lie in a flat, common plane 92 disposed at right angles to the display apparatus center line 34 and at the same time the principal planes of each of the individual projection lenses lie at right angles to the individual projection system center lines.

The structural details of the film mask 36, auxiliary masking elements 38 and film and mask holding plate 22 are shown in FIGS. 7 and 8. As shown therein the I shoulder 41 defining the detent in plate 22 in which the character mask andmasking elements are seated extends around the periphery of plate 22 with the exception of a notched portion 96 provided at the center of the base of the assembly. Film tongue 42 is centered in notched portion 96. As shown .at 98'film mask 36 is slightly shorter in its length dimension relative to masking elements 30 to allow the film to move between the two alternately selectable positions. A portion of the two selectable sets of characters on mask 36 are shown in FIG. 7. A first set of characters 102 are centered in the projection systems of the display apparatus while a second set of characters 100 are masked by elements 38 until the film mask is moved to the up position.

The use of the display apparatus of the present invention in a typical application is illustrated in FIG. 6. As shown therein terminals 104 are coupled to a control circuit 106. Control circuit 106 may include a stepping switch (not shown) which is actuated in response to operation of switch 108. The stepping switch, in turn, actuates control circuitry within circuit 106 as well as energizing a particular one of the projection systems within the display apparatus 11.

Thus, an operator on viewing a symbol on the screen 14 and thereafter pressing it in a direction indicated by arrow 110 actuates the switch 108. The actuation of the switch causes a signal to be transmitted to the control circuitry as indicated by arrow 120 and to a remote location as indicated by arrow 122. In response to the actuation of switch 108, the control circuit 106 performs certain predetermined operations. In the performance of these operations a signal indicated by arrow 124 is transmitted by control circuit 106 to selected terminals 104 to initiate the display of a new symbol on screen 14 and where required to move film mask 36.

In this manner switch 108 (means for sensing the movement of the viewing screen) is operatively associated with the projection systems in the display apparatus 11 and may be utilized to directly control the selection of symbols to be displayed on the viewing screen 14.

We claim:

1. A multiple symbol rear projection display system comprising:

a plurality of light sources disposed about a center line of the display system;

a projection screen located at the end of the system opposite the light sources;

an optical projection system located between each of the light sources and the projection screen, each system including a light collecting lens, a condensing lens and a projection lens disposed along an optical axis extending between each of the light sources and the projection screen;

means for supporting the individual light sources;

a first lens plate for supporting the individual light collecting lenses;

a second lens plate for supporting individual condensing lenses;

a third lens plate for supporting individual condensing lenses, the second and third lens plates having adjacent surfaces disposed in planes substantially perpendicular to the center line of the display system;

means for supporting the projection lenses such that the principal points of each of the projection lenses lie in a plane substantially perpendicular to the center line of the display system;

a character mask disposed in a plane on the side of the projection lenses opposite the projection screen, the character mask including pairs of characters for selective display by individual ones of the optical projection systems on the projections screen, the character mask being disposed between the adjacent surfaces of the second and third lens plates and being movable in a plane substantially perpendicular to the center line of the display system toprovide for the individual display of the characters in each pair; and

actuatable means operatively coupled to the character mask for actuating the character mask in the plane of the character mask and substantially perpendicular to the center line of .the display system between first and second positions in accordance with the selected character to be displayed, the actuatable means forming a detent bistable mechanism operating on an over-center principle and having stable characteristics in each of the first and second positions of the character mask for retaining the character mask in the actual position to provide for the individual display of the characters in each pair.

2. A display system according to claim 1 having a long focal length wherein the principal plane of each projection lens lies in a common plane perpendicular to the center line of the display system.

comprising:

long focal length wherein the principal plane of each projection lens lies in a common plane perpendicular to the center line of the display system.

3. A display system according to claim 1 having a short focal length wherein the principal plane of each projection lens lies in a plane disposed at right angles to the individual projection system center lines, the lens curvature of each of said projection lenses being varied 5 to compensate for the varying projection distance between the corresponding light source and the projection screen.

4. A multiple symbol rear projection display system a plurality of light sources disposed about a center line of the display system;

a projection screen located at the end of the system opposite the light sources;

an optical projection system located between each of the light sources and the projection screen, each system including a light collecting lens, a condensing lens and a projection lens disposed along an optical axis extending between each of the light sources and the projection screen;

means for supporting the individual light sources, light collecting lenses and condensing lenses in a spherically curved relationship relative to the light sources, light collecting and condensing lenses of each of the projection systems respectively, the center of spherical curvature being located at the center of the projection screen, the condensing lenses having first and second portions with adjacent surfaces disposed in a common plane substantially perpendicular to the center line of the display system;

means for supporting the projection lenses such that the principal points of each of said projection lenses lie in a plane perpendicular to the center line of the display system;

a character mask disposed substantially perpendicular to the center line of the display system and located on the side of the projection lenses opposite the projection screen, the character mask including at least two characters for selective display by at least one of the optical projection systems on the projection screen, the character mask being disposed between the adjacent surfaces of the first and second portions of the condensing lenses and being movable in a direction substantially perpendicular to the center line of the display system; and

actuatable means operatively coupled to the character mask for actuating the character mask in a direction substantially perpendicular to the center line of the display system between first and second positions corresponding to the display of the selected character, the actuatable means having stable characteristics in each operated position of the character mask for retaining the character mask on a stable basis in each such operated position until the next actuation of the actuatable means.

5. A display system according to claim 4 having a 6. A display system according to claim 4 having a tween the corresponding light source and the projection screen.

7. A display system according to claim 4 including means for masking the indicia projected from the character mask for preventing portions of unwanted characters from appearing on the projection screen.

8. A display system according to claim 7 wherein the masking means is an adjustable mask located at the projection screen.

9. A display system according to claim 7 wherein the masking means is a pair of auxiliary masks bracketing the character mask.

10. A projection system according to claim 9 wherein the character mask and auxiliary masks are treated such that friction between adjacent faces of said masks is reduced.

11. A backlighted display apparatus comprising:

a housing;

a viewing screen;

an optical projection system mounted within the housing for selectively projecting an image on the viewing screen, the projection system including a light source, the optical projecting system including first and second condensing lenses having surfaces disposed in spaced relationship to each other and substantially perpendicular to a center line of the display system;

a character mask having at least two character outlines disposed thereon, the character mask being disposed between the surfaces of the first and second condensing lenses and being movable in a direction substantially perpendicular to the center line of the display system;

means operatively associated with the character mask for moving the mask to selectively center individual ones of the character outlines with respect to the projection system;

mounting means coupled to the housing for mounting the viewing screen for limited movement relative to the housing in response to a force applied to the viewing screen, the mounting means including means for normally mounting the viewing screen in a predetermined position relative to the housing whereby an image is focused by the projection system 0n the viewing screen; and

means operatively associated with the viewing screen for sensing the movement of the viewing screen to actuate means for selectively energizing the projection system and the means for moving the mask.

12. A display apparatus according to claim l l including electrical switch means associated with the mounting means for actuation responsive to movement of the viewing screen.

13. A display apparatus according to claim 11 including:

a plurality of individual optical projection systems mounted within the housing; and

a character mask having a plurality of character outlines disposed therein, the plurality of outlines being greater than the plurality of projection systems.

14. A display apparatus according to claim 13 including electrical switch means associated with the mounting means for actuation responsive to movement of the viewing screen.

15. A display apparatus according to claim 13 wherein the viewing screen is mounted for pivotal movement relative to the housing, the switch means being located so as to be actuated during the pivotal movement of the viewing screen.

16. A display apparatus according to claim 15 including biasing means for returning the viewing screen after pressure is exerted thereon to the predetermined position where images are focused on the screen.

17. Display apparatus, including:

a viewing screen;

an optical projection system disposed relative to the viewing screen for selectively projecting an image on the viewing screen, the optical projecting system including first and second condensing lenses having surfaces disposed in spaced relationship to each other and substantially perpendicular to a center line of the display system;

a character mask having at least two character outlines disposed thereon, the character mask being disposed relative to the viewing screen and the optical projection system in a plane substantially perpendicular to the center line of the display system to project at least one of the character outlines on the viewing screen;

control means having first and second operative relationships and operatively coupled to the character mask and the optical projection system for selectively providing for the display by the optical projection system on the viewing screen of individual ones of the character outlines on the character mask in accordance with the operation of the control means in the first and second operative relationships, the control means having characteristics for stable operation in the first and second operative relationships to provide selectivity for the display of the individual ones of the character outlines until the next operation of the control means; and

means operatively coupled to the control means for operating upon the control means to obtain the selective operation of the control means in the first and second operative relationships and the selec' tive display by the projection system of the individ ual ones of the character outlines on the viewing screen.

18. The display apparatus set forth in claim 17 wherein the character mask is movable in the plane substantially perpendicular to the center line of the display system and wherein the control means are operatively coupled to the character mask for selectively moving the character mask in the plane substantially perpendicular to the center line of the display system to provide for the display by the optical projection system on the viewing screen of the individual ones of the character outlines.

19. In a display apparatus having a viewing screen,

a movable character mask having a planar configuration and having at least two character'outlines disposed thereon,

a pair of lens plates each having complementary curvatures to project individual ones of the character outlines on the viewing screen,

means for disposing the character mask between the lens plates in the pair for movement relative to the lens plates to provide for a projection on the viewing screen of individual ones of the two character outlines in accordance with the movements of the character mask relative to the lens plates, and

control means disposed relative to the lens plates and operatively coupled to character mask and actuable for providing a movement of the character mask relative to the lens plates to a particular position to obtain a selective projection of individual ones of the character outlines on the viewing screen,

the control means having stable characteristics in each actuation for retaining the character mask in the particular position to obtain the selective projection of the individual ones of the character outlines on the viewing screen until the next actuation of the control means.

20. In the display apparatus set forth in claim 19 the character mask being movable in a plane corresponding to its planar configuration and the control means being operable on the character mask to provide a planar movement of the character mask between individual positions in accordance with the selective projection of the individual ones of the character outlines on the viewing screen.

21. In the display apparatus set forth in claim 19, the curvatures of the lens plates being spherical.

22. In the display apparatus set forth in claim 19, each of the lens plates having a plurality of lenses at progressive positions in the curved direction and the character mask having first and second pluralities of characters, individual ones of the characters in each of the first and second pluralities being associated with individual ones of the lenses on each of the lens plates in the pair.

23. Display apparatus, including:

a viewing screen,

a plurality of light sources disposed in a particular configuration relative to the viewing screen,

a plurality of optical projection systems each disposed relative to an individual one of the light sources and the viewing screen for projecting an image on the viewing screen when its associated light source is illuminated, the plurality of optical projecting systems including first and second lens plates separated from each other in'planes substantially perpendicular to a center line of the display system, each of the first and second lens plates having a plurality of condensing lenses disposed in a curved configuration,

a character mask having first and second pluralities of characters, individual ones of the characters in the first and second pluralities being associated with individual ones of the light sources and individual ones of the optical projection systems to provide for a projection of such individual characters on the viewing screen when the associated light source is illuminated, the character mask being disposed between the first and second lens plates in a plane substantially perpendicular to the center line of the display system,

control means operatively coupled to the character mask and the optical projection system for selectively providing for the display by the optical projection systems on the viewing screen of the individual ones of the character outlines in the first plurality or in the second plurality.

24. The display apparatus set forth in claim 24 wherein the character mask is movable in the plane substantially perpendicular to the center line of the display system and wherein the control means are operatively coupled to the character mask for selectively tems on the viewing screen of the individual ones of the moving the character mask in the plane substantially character outlines in the first plurality or in the second perpendicular to the center line of the display system plurality. to provide for the display by the optical projection sys- 

1. A multiple symbol rear projection display system comprising: a plurality of light sources disposed about a center line of the display system; a projection screen located at the end of the system opposite the light sources; an optical projection system located between each of the light sources and the projection screen, each system including a light collecting lens, a condensing lens and a projection lens disposed along an optical axis extending between each of the light sources and the projection screen; means for supporting the individual light sources; a first lens plate for supporting the individual light collecting lenses; a second lens plate for supporting individual condensing lenses; a third lens plate for supporting individual condensing lenses, the second and third lens plates having adjacent surfaces disposed in planes substantially perpendicular to the center line of the display system; means for supporting the projection lenses such that the principal points of each of the projection lenses lie in a plane substantially perpendicular to the center line of the display system; a character mask disposed in a plane on the side of the projection lenses opposite the projection screen, the character mask including pairs of characters for selective display by individual ones of the optical projection systems on the projections screen, the character mask being disposed between the adjacent surfaces of the second and third lens plates and being movable in a plane substantially perpendicular to the center line of the display system to provide for the individual display of the characters in each pair; and actuatable means operatively coupled to the character mask for actuating the character mask in the plane of the character mask and substantially perpendicular to the center line of the display system between first and second positions in accordance with the selected character to be displayed, the actuatable means forming a detent bistable mechanism operating on an overcenter principle and having stable characteristics in each of the first and second positions of the character mask for retaining the character mask in the actual position to provide for the individual display of the characters in each pair.
 2. A display system according to claim 1 having a long focal length wherein the principal plane of each projection lens lies in a common plane perpendicular to the center line of the display system.
 3. A display system according to claim 1 having a short focal length wherein the principal plane of each projection lens lies in a plane disposed at right angles to the individual projection system center lines, the lens curvature of each of said projection lenses being varied to compensate for the varying projection distance between the corresponding light source and the projection screen.
 4. A multiple symbol rear projection display system comprising: a plurality of light sources disposed about a center line of the display system; a projection screen located at the end of the system opposite the light sources; an optical projection system located between each of the light sources and the projection screen, each system including a light collecting lens, a condensing lens and a projection lens disposed along an optical axis extending between each of the light sources and the projection screen; means for supporting the individual light sources, light collecting lenses and condensing lenses in a spherically curved relationship relative to the light sources, light collecting and condensing lenses of each of the projection systems respectively, the center of spherical curvature being located at the center of the projection screen, the condensing lenses having first and second portions with adjacent surfaces disposed in a common plane substantially perpendicular to the center line of the display system; means for supporting the projection lenses such that the principal points of each of said projection lenses lie in a plane perpendicular to the center line of the display system; a character mask disposed substantially perpendicular to the center line of the display system and located on the side of the projection lenses opposite the projection screen, the character mask including at least two characters for selective display by at least one of the optical projection systems on the projection screen, the character mask being disposed between the adjacent surfaces of the first and second portions of the condensing lenses and being movable in a direction substantially perpendicular to the center line of the display system; and actuatable means operatively coupled to the character mask for actuating the character mask in a direction substantially perpendicular to the center line of the display system between first and second positions corresponding to the display of the selected character, the actuatable means having stable characteristics in each operated position of the character mask for retaining the character mask on a stable basis in each such operated position until the next actuation of the actuatable means.
 5. A display system according to claim 4 having a long focal length wherein the principal plane of each projection lens lies in a common plane perpendicular to the center line of the display system.
 6. A display system according to claim 4 having a short focal length wherein the principal plane of each projection lens lies in a plane disposed at right angles to the individual projection system center lines, the curvature of each of said projection lenses being varied to compensate for the varying projection distance between the corresponding light source and the projection screen.
 7. A display system according to claim 4 including means for masking the indicia projected from the character mask for preventing portions of unwanted characters from appearing on the projection screen.
 8. A display system according to claim 7 wherein the masking means is an adjustable mask located at the projection screen.
 9. A display system according to claim 7 wherein the masking means is a pair of auxiliary masks bracketing the character mask.
 10. A projection system according to claim 9 wherein the character mask and auxiliary masks are treated such that friction between adjacent faces of said masks is reduced.
 11. A backlighted display apparatus comprising: a housing; a viewing screen; an optical projection system mounted within the housing for selectively projecTing an image on the viewing screen, the projection system including a light source, the optical projecting system including first and second condensing lenses having surfaces disposed in spaced relationship to each other and substantially perpendicular to a center line of the display system; a character mask having at least two character outlines disposed thereon, the character mask being disposed between the surfaces of the first and second condensing lenses and being movable in a direction substantially perpendicular to the center line of the display system; means operatively associated with the character mask for moving the mask to selectively center individual ones of the character outlines with respect to the projection system; mounting means coupled to the housing for mounting the viewing screen for limited movement relative to the housing in response to a force applied to the viewing screen, the mounting means including means for normally mounting the viewing screen in a predetermined position relative to the housing whereby an image is focused by the projection system on the viewing screen; and means operatively associated with the viewing screen for sensing the movement of the viewing screen to actuate means for selectively energizing the projection system and the means for moving the mask.
 12. A display apparatus according to claim 11 including electrical switch means associated with the mounting means for actuation responsive to movement of the viewing screen.
 13. A display apparatus according to claim 11 including: a plurality of individual optical projection systems mounted within the housing; and a character mask having a plurality of character outlines disposed therein, the plurality of outlines being greater than the plurality of projection systems.
 14. A display apparatus according to claim 13 including electrical switch means associated with the mounting means for actuation responsive to movement of the viewing screen.
 15. A display apparatus according to claim 13 wherein the viewing screen is mounted for pivotal movement relative to the housing, the switch means being located so as to be actuated during the pivotal movement of the viewing screen.
 16. A display apparatus according to claim 15 including biasing means for returning the viewing screen after pressure is exerted thereon to the predetermined position where images are focused on the screen.
 17. Display apparatus, including: a viewing screen; an optical projection system disposed relative to the viewing screen for selectively projecting an image on the viewing screen, the optical projecting system including first and second condensing lenses having surfaces disposed in spaced relationship to each other and substantially perpendicular to a center line of the display system; a character mask having at least two character outlines disposed thereon, the character mask being disposed relative to the viewing screen and the optical projection system in a plane substantially perpendicular to the center line of the display system to project at least one of the character outlines on the viewing screen; control means having first and second operative relationships and operatively coupled to the character mask and the optical projection system for selectively providing for the display by the optical projection system on the viewing screen of individual ones of the character outlines on the character mask in accordance with the operation of the control means in the first and second operative relationships, the control means having characteristics for stable operation in the first and second operative relationships to provide selectivity for the display of the individual ones of the character outlines until the next operation of the control means; and means operatively coupled to the control means for operating upon the control means to obtain the selective operation of the control means in the first and second operative relationships and The selective display by the projection system of the individual ones of the character outlines on the viewing screen.
 18. The display apparatus set forth in claim 17 wherein the character mask is movable in the plane substantially perpendicular to the center line of the display system and wherein the control means are operatively coupled to the character mask for selectively moving the character mask in the plane substantially perpendicular to the center line of the display system to provide for the display by the optical projection system on the viewing screen of the individual ones of the character outlines.
 19. In a display apparatus having a viewing screen, a movable character mask having a planar configuration and having at least two character outlines disposed thereon, a pair of lens plates each having complementary curvatures to project individual ones of the character outlines on the viewing screen, means for disposing the character mask between the lens plates in the pair for movement relative to the lens plates to provide for a projection on the viewing screen of individual ones of the two character outlines in accordance with the movements of the character mask relative to the lens plates, and control means disposed relative to the lens plates and operatively coupled to character mask and actuable for providing a movement of the character mask relative to the lens plates to a particular position to obtain a selective projection of individual ones of the character outlines on the viewing screen, the control means having stable characteristics in each actuation for retaining the character mask in the particular position to obtain the selective projection of the individual ones of the character outlines on the viewing screen until the next actuation of the control means.
 20. In the display apparatus set forth in claim 19 the character mask being movable in a plane corresponding to its planar configuration and the control means being operable on the character mask to provide a planar movement of the character mask between individual positions in accordance with the selective projection of the individual ones of the character outlines on the viewing screen.
 21. In the display apparatus set forth in claim 19, the curvatures of the lens plates being spherical.
 22. In the display apparatus set forth in claim 19, each of the lens plates having a plurality of lenses at progressive positions in the curved direction and the character mask having first and second pluralities of characters, individual ones of the characters in each of the first and second pluralities being associated with individual ones of the lenses on each of the lens plates in the pair.
 23. Display apparatus, including: a viewing screen, a plurality of light sources disposed in a particular configuration relative to the viewing screen, a plurality of optical projection systems each disposed relative to an individual one of the light sources and the viewing screen for projecting an image on the viewing screen when its associated light source is illuminated, the plurality of optical projecting systems including first and second lens plates separated from each other in planes substantially perpendicular to a center line of the display system, each of the first and second lens plates having a plurality of condensing lenses disposed in a curved configuration, a character mask having first and second pluralities of characters, individual ones of the characters in the first and second pluralities being associated with individual ones of the light sources and individual ones of the optical projection systems to provide for a projection of such individual characters on the viewing screen when the associated light source is illuminated, the character mask being disposed between the first and second lens plates in a plane substantially perpendicular to the center line of the display system, control means operatively coupled to the character mask and The optical projection system for selectively providing for the display by the optical projection systems on the viewing screen of the individual ones of the character outlines in the first plurality or in the second plurality.
 24. The display apparatus set forth in claim 24 wherein the character mask is movable in the plane substantially perpendicular to the center line of the display system and wherein the control means are operatively coupled to the character mask for selectively moving the character mask in the plane substantially perpendicular to the center line of the display system to provide for the display by the optical projection systems on the viewing screen of the individual ones of the character outlines in the first plurality or in the second plurality. 